Boy I hope so I'm doing 30 racks and 75 thighs just that way next week.
Seriously though you can absoluetly do this. Generally whenever I fire up The Big Heavy it is most often for chicken and ribs for a cookout. I do just as what was said start the ribs first (time depends on babybacks or spares) and then start the chicken about 4 hours to serve time. I try to cook the chicken at the hottest spot on the grill to help crisp the skin, because it does need heat to get crispy.
I also goose the heat in general for the last 30 minutes or so. By then I glazing my ribs so the extra heat is not bad and I'm starting to pull and cut them anyway. So the extra heat can't hurt the ribs but greatly helps the chicken.